1. Field of the Invention
The present invention relates to a liquid crystal display device and, in particular, to a liquid crystal display device suitable for use in an ECB type color liquid crystal display which effects multi-color display using ECB (electrically controlled birefringence) effect.
2. Description of the Related Art
Conventionally, there has been available, as an LCD (liquid crystal device) having a simple construction and capable of stable multi-color display, an ECB type color liquid crystal device, in which the birefringence of a liquid crystal cell is controlled by applying an electric field thereto.
This color liquid crystal display device effects color display by utilizing the birefringence effect provided by a liquid crystal cell using an STN (super-twisted nematic) molecular arrangement in which the dielectric anisotropy is positive (or negative) and in which the twisting angle is 180 to 360 degrees.
FIG. 3 is a sectional view showing an example of a conventional ECB type semi-transmissive liquid crystal display device.
In this semi-transmissive liquid crystal display device 1, an STN type liquid crystal cell 5 is formed by an STN liquid crystal layer 2, and upper and lower glass substrates 3 and 4 opposed to each other through the intermediation of the STN liquid crystal layer 2. An upper polarizing plate 6 is provided on the upper side of this liquid crystal cell 5, and a lower polarizing plate 7 is provided under it. A semi-transmissive plate 8 and a backlight 9 are provided below the lower polarizing plate 7.
On the lower side of the upper glass substrate 3, an upper transparent electrode 11 and an upper orientation layer 12 are stacked together, and on the upper side of the lower glass substrate 4, a lower transparent electrode 13 and a lower orientation layer 14 are stacked together. The STN liquid crystal layer 2 is sealed in the region defined by the upper orientation layer 12 and the lower orientation layer 14.
In this semi-transmissive liquid crystal display device 1, an attempt is made to use a semi-transmissive film instead of the semi-transmissive plate 8 to achieve a further reduction in thickness.
Unlike other types of liquid crystal display device, this semi-transmissive liquid crystal display device 1 uses no color filter, so that there is no deterioration in light transmittance and it is possible to make the screen bright, with the power consumption being reduced.
However, the above-described conventional semi-transmissive liquid crystal display device 1 has a problem in that if a semi-transmissive film is used instead of the semi-transmissive plate 8, the display is reversed when transmitted light from the backlight 9 is used (i.e., when the device is used as a transmission type liquid crystal display device) although the display when reflected light is used (i.e., when the device is used as a reflection type liquid crystal display device) is normal.
The reversal of the display in the case of transmitted light is a serious problem in the semi-transmissive liquid crystal display device 1, so that the semi-transmissive film has not taken the place of the semi-transmissive plate 8 yet.